Genes beginning with "r"

All
eight ascospores of heterozygous R/R+ asci are round rather than
ellipsoid (Fig. 56). R is thus
nonautonomous (or nearly so) in ascospores and dominant in the ascus (1367). Ascospores are round
even in nonlinear asci (1546, 1966). A single germination pore is formed in spores that are
completely
round, two pores in spores that are slightly ovoid (1483a). Vegetative morphology is abnormal,
somewhat resembling that of peach. Initial growth on a slant is concentrated around the
inoculation
point. The vegetative morphology is recessive in heterozygous duplications, such as those from
T(NM103) (2123). Female sterile with no perithecia, but R ´
R crosses are productive if R is
heterokaryotic in the female parent (1962). Used to study duplication instability (2123) and to show that
ascospore development is autonomous in individual asci of different genotype within the same
perithecium (999). Used to show that defective asci in crosses between inbred
strains do not result from
self-fertilization of mat A ´ mat A or
mat a ´ mat a (1687). Recurrences have been obtained (1962,
1966). Although the R locus is not included in duplications from T(MD2)
´ Normal, roundascospores
that appear to carry new R mutations are found among the progeny of crosses in which
one parent is the
breakdown product of such a duplication (978). For other genetically determined round ascospores, see
ref. (117). Called Rsp (1966), but the original symbol R has priority. [The symbol
rsp has been used for
cytoplasmically determined respiration-deficient mutants (1741)].

FIGURE 56 (A) Asci from a cross of wild type X Round spore. The Round spore
mutation is
ascus-dominant: all eight ascospores (R as well as R+) are round. (B) Asci from a cross
between two
wild-type strains, for comparison. The asci with unpigmented or lightly pigmented spores are
immature.
Bar length = 50 mm. Photographs by N. B. Raju.
From refs.
(1676 ) and
(1680 ),
with permission from Urban & Fischer Verlag and from
the British Mycological Society,
respectively.

Prevents killing by Sk-2 of ascospores that are not themselves Sk-2. Does
not confer resistance to killing
by Sk-3. Allelism of r(Sk-2) with Sk-2 is not excluded because
recombination in this region is blocked
when Sk-2 is heterozygous. Recombination is not blocked by r(Sk-2)-1. Allele
P527 was found in
Neurospora crassa from Louisiana. Only one other known N. crassa wild type is
resistant (2121). For
reference strains and tester strains for identifying the various killers and genes conferring
resistance to
killing, see refs. (2127) and (2128).

Prevents killing by Sk-3of ascospores that are not themselves
Sk-3. Does not confer resistance to killing
by Sk-2. Allelism of r(Sk-3) with Sk-3 is not excluded because
recombination in this region is blocked
when Sk-3 is heterozygous. Recombination is not blocked by r(Sk-3). Found in
Neurospora intermedia
and introgressed into Neurospora crassa (2121). For reference strains and tester strains for identifying
the various killers and genes conferring resistance to killing, see refs. (2127) and (2128).

Radiation
Sensitivity

See
Mei-2, mei-3, mus, nuh-4, phr, upr-1, uvs. The
symbol rad has not been used in Neurospora.

Genes
belonging to the ras supergene family (named for an oncogene of the rat sarcoma virus)
encode
highly conserved G proteins that are important for signal transduction pathways regulating
growth and
differentiation. The Neurosporaras-like genes called ras, krev, and
ypt have been identified as ras-like
by DNA sequence homologies. When phenotypes are examined using null mutants obtained by
RIP, ras-like genes may prove to be allelic with already known mutants (e.g., the gene
originally designated ras-2
proved to be allelic with smco-7).

The
Myb-like functional homolog of flb1 in Aspergillus nidulans. The
Neurospora gene complements
the sporulation defect of the Aspergillus mutant, but a deletion mutant has no visible
effect on growth or
conidiation in Neurospora other than to make early hyphal growth counter-clockwise or
straight, in
contrast to the typically clockwise spiral growth of Neurospora wild type (see Spiral
Growth) (1902).

Genes
specifying 5.8S, 17S, and 25S ribosomal RNA (but not 5S) are located in the NOR in a series of
~150 tandem repeats, each ~9.3 kb long. The repeats are separated by nontranscribed spacers (423, 672).
rDNA is a site of chromosome breakage in the breakdown of duplication strains derived
from
translocations that involve the NOR (261). See NOR.

trans-acting genes that regulate meiotic recombination in specific regions and
constitute a class of
recombination control genes first described in Neurospora (339, 990) (Fig. 57). Initially detected by
changed intragenic recombination (up to 25´), but crossing over
between loci may also be affected (up to
40X). High recombination is recessive. Products of dominant alleles (called
rec+) are thought to repress
the initiation of recombination at specific recombinator loci, of which cog is a
well-studied example. A
given target locus or region appears to be affected specifically by alleles at only one rec
locus. Polarity of
intragenic recombination in a target locus may be changed by the presence of the controlling
rec+ allele.
Control of recombination is independent from the control of gene expression (311). Three rec loci have
been identified and characterized. Ten are estimated to be present in the Neurospora crassa
genome.
Differences at rec loci are present in commonly used laboratory wild types (338). For reviews, see refs.
(316), (335), and (645).

FIGURE 57 Linkage map showing the location and targets of action of rec-1, rec-2, and
rec-3.
Original figure from D. E. A. Catcheside.

Presence of allele rec-1+ reduces recombination within the loci
his-1 (VR) (990, 2083) and nit-2 (IL)
(320, 324) (Fig. 57), but does not affect recombination at other his
loci (314). A recessive allele from
another lineage was called rec-z until it was identified as rec-1 (324).

Presence of dominant allele rec-2+ reduces recombination within the
his-3 locus (IR) and reduces crossing
over in the intervals pyr-3 to his-5 (IVR), his-3 to ad-3 (IR), and
arg-3 to sn (IL) (336, 338, 1930) (Fig.
57). Interacts with cog in affecting recombination in his-3 and crossing over
between his-3 and ad-3 (45,
336). Used in conjunction with translocation T(TM429) his-3 to demonstrate that
cog+ acts only in cis in
affecting recombination between sites in his-3 (336). (See cog.) Recessive rec-2 alleles from other
lineages were called rec-4, rec-5, or rec-w until identity was demonstrated (333).

Presence of allele rec-3+ reduces recombination within the loci
his-2 (IR) and am (VR) but not within
gul-1, which shows <0.3% recombination with am (337, 1940, 1941). Crossing over is also reduced in
the interval between sn and his-2 (338) (Fig. 57). Three alleles are known: rec-3,
rec-3L, and rec-3+
(334). A recessive allele from another lineage was initially called
rec-x (333).

IR.
Linked to mat (15%), rg-1 (0/650) and left of lys-4 (12%) after
introgression into Neurospora crassa
(1546).

Altered
phosphoglucomutase (EC 5.4.2.2) (isozyme II) (1357). Morphology is similar to rg-1 (1359).
Found in a Neurospora sitophila cross that was heterozygous for an rg-1 allele
from N. crassa.
Interpreted from its behavior in N. sitophila to be unlinked to rg-1 or to
su(rg-2) (1359).

Putative
structural gene for rehydrin (thiol-specific antioxidant, peroxiredoxin, dormancy-associated
protein, non-selenium glutathione peroxidase, EC 1.11.1.7). The preceding ESTs define the 5'
and 3' ends
of a transcript with homology to a region in linkage group VII contigs (EMBL/Genbank
AC006498;
1041). The sequence shows high homology to the rehydrin gene, which is highly conserved from
cyanobacteria to higher plants and animals. Consistent with the probable involvement of an
rhd gene in
dormancy, the sequence is found in a subtracted conidial cDNA library (1448).

Only
two rib loci are known in Neurospora, compared to six that have been assigned to
biosynthetic steps
in Saccharomyces (522). Supplemented medium should be shielded from light to avoid
the destruction of
riboflavin.

Requires riboflavin (1361). Used to examine the role of flavin as a photoreceptor for
carotenogenesis and
for the phase-shifting and suppression of circadian conidiation (1513). Allele 51602 is heat-sensitive (34
vs 25ºC), but allele C106 is not (717).

Scored
as an irreparable heat-sensitive mutant (34 vs 25ºC). Attains 2% of the wild-type linear
growth
rate at 35ºC and 80% at 25ºC (1755). Conditional defect in the accumulation of 25S rRNA and,
hence,
60S cytosolic ribosomal subunits (1219, 1221, 1222, 1755). Defective ribosome biosynthesis is attributed
to a defect in rRNA processing (1222). At restrictive temperature, conidia survive and apolar growth
results in highly multinucleate spherical cells, with no hyphae on glycerol complete agar medium
(1546,
1751). Messenger RNA synthesis is normal at 37ºC. Good fertility, growth, and viability
at 25ºC make
rip-1 preferable to un-15 as a marker for the right end of II. The original strain
carrying both rip-1 and inl
was called 4M(t), and the rip-1 allele was designated 1(t).

Morphologically similar mutants, so named because the hyphae form ropelike aggregates
that grow up the
tube wall from agar slants, producing conidia in dense clumps at the top (1548). Hyphae are excessively
branched and curled (248, 719). Microscopic analysis reveals defects in conidial germination,
placement
of septa, and mitochondrial morphology (1348). ropy mutants function as fertilizing parents, but are
female-infertile unless complemented in a heterokaryon with ro+. None of
the ropy genes has been found
to be essential for viability [see, for example, ref. (2093)]. Nuclear distribution in hyphae is abnormal as
a result of defects in a microtubule-associated motor (248, 1634, 1729). Mutations at various ropy loci
can be selected as partial suppressors of cot-1 [248, 1637; reviewed in ref. (2258)]. Some combinations
of allelic mutations show complementation between alleles, whereas some mutations at different
ropy loci
fail to complement one another (248). Unlinked noncomplementation most often involves ro-1
or ro-3.

Morphology is typical ropy. Encodes the heavy chain of cytoplasmic dynein, a
minus-end-directed motor
molecule. Some combinations of alleles show complementation and may fail to complement
some alleles
at other ropy loci (248). Used to examine the kinesin-dynein (kin; ro-1) double
mutant, which is
defective in oppositely directed microtubule motors, and to compare it with the single mutants
(1871).
Photographs (507, 1626). The amount of cell-wall peptides is reduced (2249). Growth is limited on
glycerol medium (419).

Encodes a novel 80-kDa protein that has two cysteine-rich motifs that resemble
zinc-binding LIM or
RING domains thought to mediate protein-protein interactions. Mutations obtained by RIP
inactivation
are defective in nuclear migration and are blocked in conidiation (2155).

Encodes the largest subunit of the dynactin complex (P150Glued), which is
not essential for viability but is
required for normal nuclear distribution (2093). Some combinations of alleles show complementation
and may fail to complement some alleles at other ropy loci (248). Photograph (248). Growth is limited
on glycerol medium (419). The Spitzenkörper is undetectable or difficult to detect by
phase contrast
(1727). Called cfl on the map in ref. (1585).

Encodes a novel 70-kDa actin-related protein (1347). The large subunits of cytoplasmic dynein and
dynactin accumulate at spindle pole bodies in the mutant (1347). Growth is inhibited on glycerol medium
(419). Female sterile, contrary to a misprint in ref. (1584).

The
validity of the available strain, R2526, is suspect. It is not morphologically ro and is
indistinguishable from da. Conidia of R2526 are normal sized, unlike tng. The
mutant may have been
misidentified and misnamed (unlikely), the original may have been a double mutant from which
the ropy
component was lost, or a stock may have been mislabeled (1567).

Encodes a novel 24-kDa protein that may be necessary for dynactin stability (1347). Ascospores from
rearrangement Slm-1 ´ Normal
include a class that is deficient for a short terminal segment containing ro-10. The
deficiencyprogeny germinate and die unless they are rescued in a heterokaryon. The
rescued
deficiency can be transmitted through a cross (114).

Spreading colonial morphology, with conidiating tufts. Grows better on sucrose minimal
medium than on
glycerol complete (1548). Formerly called mat. The name was changed to
rug so that mat could be used
as the symbol for mating type, in conformity with usage in other fungi (745).